The canvas covered the lower portion of the barco, or hanging choir, from whose grated windows the enclosed nuns would follow the religious services. The tale, punctuated by faux stucco frames embellished with gold ribbons, vine shoots, and fruit festoons, is articulated by a series of characters in audacious poses. The biblical episode of the bronze serpent, lifted on a rod by Moses to save the Jewish people from the scourge of venomous serpents sent by the Lord, is interpreted with tragic emphasis and extraordinary pictorial licence.